In typical repeatered buried or undersea telecommunications or telemetric cable systems, the cable is designed to have substantial cross-section for strength and robustness. The electrical conductor of the cable may therefore be large without adversely affecting the overall cable characteristics. The cable conductor has relatively low resistivity, on the order of 0.5-2 ohms per kilometer. The repeaters are powered by placing them in series with the cable conductor and feeding the power from a constant current source which provides for a small voltage drop across each repeater.
In response to demand for less costly and more readily deployable cable systems, cable designs of substantially reduced diameter have been introduced. These systems use substantially less conductor for power transmission. The resistivity of such cables thus is substantially greater than earlier designs, on the order typically of 20 ohms per kilometer. Such a cable is less capable of carrying electrical power because to deliver the wattage required by the amplifiers requires an increase in the source voltage that necessitates an increase in the polyethylene dielectric strength. Adding polyethlene thickness to provide dielectric strength is, of course, incompatible with achieving the small overall cable diameter. Moreover, high voltages transmitted over small diameter cables cause cable failures more frequently at points where the cable sheathing may be kinked or damaged. As a result, the maximum length of small diameter undersea or terrestrial cable systems has been limited.